The present invention relates to a constant current-constant voltage circuit, and in particular to a constant current-constant voltage circuit in a semiconductor integrated circuit including integrated MOSFETs.
A reference voltage generator as shown in FIG. 2 is disclosed in U.S. Pat. No. 4,454,467 corresponding to Japanese patent application laid-open No. JP-A-58-22423.
That is to say, the known reference voltage generator shown in FIG. 2 includes N-channel MOSFETs Q.sub.1 and Q.sub.2 having gates connected together, an N-channel MOSFET Q.sub.3 having a gate connected to its drain, and P-channel MOSFETs Q.sub.4 and Q.sub.5 forming a current mirror circuit. The threshold voltage V.sub.th1 of the N-channel MOSFET Q.sub.1 is so set as to have a large value whereas the threshold voltage V.sub.th2 of the N-channel MOSFET Q.sub.2 is so set as to have a small value. Therefore, it is possible to derive a threshold voltage difference V.sub.th1 -V.sub.th2 =.DELTA.V.sub.th at an output terminal T.sub.o as output voltage V.sub.out.
This threshold voltage difference .DELTA.V.sub.th obtained at the output terminal T.sub.o becomes constant irrespective of a change in supply voltage V.sub.DD and a temperature change.